SIM-Assisted End-to-End Co-Frequency Co-Time Full-Duplex System

To further suppress the inherent self-interference (SI) in co-frequency and co-time full-duplex (CCFD) systems, we propose integrating a stacked intelligent metasurface (SIM) into the RF front-end to enhance signal processing in the wave domain. Furthermore, an end-to-end (E2E) learning-based signal processing method is adopted to control the metasurface. Specifically, the real metasurface is abstracted as hidden layers of a network, thereby constructing an electromagnetic neural network (EMNN) to enable driving control of the real communication system. Traditional communication tasks, such as channel coding, modulation, precoding, combining, demodulation, and channel decoding, are synchronously carried out during the electromagnetic (EM) forward propagation through the metasurface. Simulation results show that, benefiting from the additional wave-domain processing capability of the SIM, the SIM-assisted CCFD system achieves significantly reduced bit error rate (BER) compared with conventional CCFD systems. Our study fully demonstrates the potential applications of EMNN and SIM-assisted E2E CCFD systems in next-generation transceiver design.

Dual-Polarization Stacked Intelligent Metasurfaces for Holographic MIMO

To address the limited wave domain signal processing capabilities of traditional single-polarized stacked intelligent metasurfaces (SIMs) in holographic multiple-input multiple-output (HMIMO) systems, which stems from limited integration space, this paper proposes a dual-polarized SIM (DPSIM) architecture. By stacking dual-polarized reconfigurable intelligent surfaces (DPRIS), DPSIM can independently process signals of two orthogonal polarizations in the wave domain, thereby effectively suppressing polarization cross-interference (PCI) and inter-stream interference (ISI). We introduce a layer-by-layer gradient descent with water-filling (LGD-WF) algorithm to enhance end-to-end performance. Simulation results show that, under the same number of metasurface layers and unit size, the DPSIM-aided HMIMO system can support more simultaneous data streams for ISI-free parallel transmission compared to traditional SIM-aided systems. Furthermore, under different polarization imperfection conditions, both the spectral efficiency (SE) and energy efficiency (EE) of the DPSIM-aided HMIMO system are significantly improved, approaching the theoretical upper bound.